Year	Percent
1997	2.9
1998	2.8
1999	2.7
2000	3.5
2001	3.4
2002	3.2
2003	3.6
2004	3.7
2005	3.5
2006	3.4
2007	3.4
2008	3.8
2009	4
2010	4.3
2011	4.4
2012	4.3
2013	4.5
2014	4.7
2015	4.7
2016	4.6